The essay deals with the role of the American (but Italian-born) political scientist Mario Einaudi in the development of comparative politics after World War II. The author focuses his attention on Einaudi's most important experience in political research, the French-Italian Inquiry he carried out with several European collaborators between 1948 and 1955, and on some general preliminary presentations of his analytical framework. Such reconstruction highlights both Mario Einaudi's important contribution in re-shaping the field of European comparative politics according to the suggestions of area studies. It also points out Einaudi's use of Les parti politiques recently published by Maurice Duverger to present new Italian and French mass parties in a genuine pattern of comparison with American parties, in a significant attempt to consolidate «denationalization» of intellectual debate on the topic.